Isochromatic photographic plate and film.



NQ. 746,594. PATENTED DEG. a, 1903.'

L. SMITH. N

ISVDGHROMATIC PHOTOGRAPHIG PLATE AND FILM.

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'mi wonms Pnzns cu. Pxomum'o.. wAsmNo'rou. o. c.

*UNiTED ISTATES,

Patented December 8, 1903. f

'PATENT OFFICE.

LEONARD SMITH, OF LONDON, ENGLAND.

SPECIFICATION forming part of Letters Patent N o. 746,594, datedDecember 8, 1903.

Serial No. 146,207. (No model.)

To a/ZZ whom it may concern:

Be it known that I, LEONARD SMITH, manufacturing chemist, a subject ofthe King of Great Britain, residing at 14 West Hill, Highgate, London,England,have invented certain new and useful Improvementsin IsochromaticPhotographic Plates and Films, of which the following is aspecification.

As is well known in photography, the tonerendering and modelingqualities of the ordinary sensitive emulsion are extremely imperfeet,and one method of correcting this defect is by treating the emulsionwith organic dyes, whereby the sensitiveness of the emulsion to the red,green, and yellow rays is greatly increased; but such an emulsion doesnot afford an improved tone-renderin g when the subject exhibitscontrasts; and the present invention has for its object to produce anisochromatic color-sensitive film whereby a more perfect modeling and amore correct color-rendering may be obtained.

In the accompanying drawing, forming a part of this specification, thefigure represents asectional view of a support and the ilm carriedthereby.

In order to accomplish the desired result, a suitable support C isemployed,on which is arranged the film, consisting of two or moresuperimposed color-sensitive emulsions B A of progressivelyvaryingdegrees of sensitiveness and color sensitiveness, so that when thecomposite rays fall on the topmost layer of most highly color-sensitiveemulsion the latent image will be formed in that layer, and as theexposure is continued the most powerful rays, or those which produce theextreme high lights, alone will penetrate to a greater depth. In thecase of an ordinary film these rays would spread over the sensitiveemulsion, thereby impairing correct tonal relation, and, moreover, partof these rays would be reiiected by the surface of the support by whichthe sensitive film is carried and would thereby cause halation, whereasin the case of a sensitive iilm made according to thisinvention thepresence of the less sensitive coating or coatings of color-sensitiveemulsion underlying the layer first acted on will have the effect ofcausing these harmful rays to be absorbed. Even underprolonged exposurethe complete penetration of the composite rays will be prevented andcorrect tonal relation will be maintained in the several superimposedlayers of colorsensitive emulsion. Thus the correct relative value ofall tones in the negative will be preserved and no rays will bepermitted to pass completely through the composite film composed ofseveral superimposed layers of sensitive emulsion.

In carrying theinvention into eect the two emulsions are to be renderedcolor sensitive by a definite percentage of the potassium salt oftetraiodid of iiuorescin and the proportions of which are different inthe slow and fast emulsion, the quantities being in the fast film forevery one hundred parts of silver bromid .12 parts and in the slow film.O6 parts. The sloweremulsion having ,been applied as a first layer B onthe support C and dried, the faster emulsion, made in the same manner,but diering from the rst only in its higher degree of sensitiveness tothe actinic rays, is then applied as a second coating A on top of thefirst or slower coating and allowed to dry, and so on for as manysuperimposed coatings of progressively-increasing degrees ofsensitiveness as may be deemed necessary to insure the completeinterception of the rays. A

I am aware that a lm composed of a single layer of isochromatic emulsionand a film composed of two or more superimposed layers of ordinarynon-isochromatic emulsion are known, and I do not lay any claim toeither separately. v

The advantages obtained by this invention as compared with the ordinarysingle layer of isochromatic emulsion is the absence of all halation andfalse tone-rendering due to imperfect interception of light-rays and ascornpared with a double or triple layer of ordinary emulsion the widerand more perfect tone-rendering due to the color sensitiveness of eachlayer of emulsion of which the film of this invention is composed.

I claiml. As a new article of manufacture, an isochromatic photographiclmformed of successively-superimposed layers of color-sensitive emulsionhaving progressively-varying degrees of sensitiveness andcolor-sensitiveness, as speciied. y

2. As a new article of manufacture, an iso- IOO chromatic photographicfilm formed of sucunderlying slow lm 'containing the lesser`cessively-superimposed layers of color-sensiand the superimposed fasterfilm the higher tive emulsion. having progressively-varying percentageof the said salt, as specified.

degrees of sensitiveness, and which have been LEONARD SMITH. 5 renderedcolor sensitive by the incorporation Witnesses:

therewith of the potassium sait of tetraiodid C. G. CLARK,

of fiuorescin, in different proportions, the 1 T. W. KENNARD.

